I notice that the font sizes in the Arduino IDE are not at all consistent with font point sizes in the rest of Ubuntu/Gnome 10.04. For instance, font Droid Sans Mono, plain, size 12 in Arduino is much smaller than 12 point Droid Sans Mono is in every other application.

I may have to take a look at this myself since no one is fixing it and it's terribly ugly without antialiasing.

Even though I didn't have any problem in Ubuntu 9.10 I did notice problems in 10.04 and with the default font size, the _'s are not displaying properly. But after increasing the font size to 14, everything looks pretty good.